About 2% of children develop a type of relative blindness in one eye known as functional amblyopia - a deficit in central visual acuity for which no obvious optical or pathological cause can be determined. The structures of the visual system that are affected and the ways they are altered are not fully known. Treatment of functional amblyopia, no longer believed to be limited to children under 6 years, is nonetheless only partially effective for most patients. The present application requests renewal of a grant (1-R01-EY02125) that supported the successful development of an auditory-feedback technique that has now been shown to produce steady and foveal fixation of eccentrically fixating amblyopic eyes. Using this feedback technique, several fundamental questions about the sensory and motor mechanisms of amblyopia have been answered. With the proposed renewal support, sensory and motor mechanisms of vision will be investigated with the aim of testing a central hypothesis: "Most, if not all of the sensory deficits (e.g., visual acuity, contrast sensitivity, spatial summation) and oculomotor abnormalities (e.g., unsteady fixation, eccentric fixation, poor smooth and saccadic tracking) are explained by the aberrated or distorted space sense present in a central retinal region of functionally amblyopic eyes." Of the eight specific aims and "experiments" that stem from this hypothesis, six will be performed in the laboratory and two will be conducted in a clinic setting; the latter will involve a) development of a clinically applicable battery of tests to evaluate functional amblyopia in each of its basic deficits, and b) develop clinically applicable feedback training procedures that efficiently promote steady, foveal fixiation and foveal directionalization in functionally amblyopic eyes.